Heavy over-the-road vehicles including tractor trailer trucks and the like require a suspension to support its chassis from one or more axles. The demands on these suspension systems are quite great as, among other things, they must have springs with sufficient rigidity to withstand the heavy loads carried by these vehicles, they must stabilize the axle and prevent wind up or wheel hopping as the brakes are applied, and, for multiple axle vehicles, they must distribute the weight by shifting excess loading from one axle to another to thereby balance the load over the axles. A suspension should be relatively easy to install and should provide a way to adjust the axle height and longitudinal placement of the axles with respect to the chassis to ensure proper wheel and axle alignment. Another requirement is that the suspension provide an ease of maintenance including a design which facilitates the replacement of springs or any other component which is subject to wear or possible damage. Preferably, the suspension should permit as much repair or maintenance as is possible without removing or disassembling it from the vehicle.
Invariably, leaf spring suspension assemblies of the prior art utilize axle mounts having U-bolts or some other means to rigidly secure the leaf spring to the axle. This construction helps to stabilize the axle but makes it more difficult to remove and install the leaf spring and also, for multiple axle vehicles, hinders relative lateral movement of the leaf spring with respect to the axle as an aid in balancing the load amongst the axles. An example of a leaf spring suspension assembly which has an axle mount positively securing the spring to the axle is disclosed in applicant's own U.S. Pat. No. 3,499,660, issued Mar. 10, 1970, incorporated herein by reference. Applicant's patented suspension represents a significant improvement over the prior art by providing many advantages previously unavailable. Some of these are leaf spring ends which are free, shifting of the load being accomplished through the rotatably mounted equalizer which can tilt in either direction should an unequal force be applied by the spring ends resting on bearing pads supported at opposite ends of the equalizer. Thus, applicant's prior patented suspension is an excellent one which utilizes leaf springs clamped to the axle and which provides unique advantages over the prior art.
In the first embodiment of applicant's invention described herein, a unique torque rod and axle mount provide a means to stabilize the axle without requiring that it be positively clamped or otherwise secured to the leaf spring itself. Thus, the leaf spring is freed up and is permitted to slide laterally across the axle in response to varying loads as an aid in balancing the load between axles in a multiple axle vehicle. Furthermore, this unique axle mount reduces the amount of time required to install the suspension and also the amount of time required to replace a leaf spring. Many of the same advantages of applicant's prior patented suspension are carried over into applicant's present invention and include the vertically adjustable bearings supporting the leaf spring ends, the vertically adjustable equalizer, adjustable length torque rods, a rotatably mounted equalizer, and other advantages as described in applicant's prior patent, mentioned above. In addition to these, the leaf springs of the present invention are free floating and have a "camel-back" or curvilinear medial section which approximates the curvature of the axle and rests on a wear pad made of nylon or the like. A roller assembly mounts above the curvilinear portion and rolls along the spring as it moves laterally with respect to the axle. The change in curvature of the leaf spring serves as a stop which prevents excess lateral movement or over-shifting of the spring.
The torque rod and axle bracket assembly utilize two pivotal connections at the axle and a resilient pivotal connection between the torque rod and a hanger to provide unrestricted vertical deflection of the axle with respect to the chassis with a limited oscillation of the axle about the chassis. The capability for limited oscillation of the axle is provided by the resilient pivotal connection of the torque rod to the hanger, and has been previously described in applicant's U.S. Pat. No. 3,081,086 issued Apr. 2, 1974, incorporated herein by reference.
In applicant's second embodiment, all the advantages of applicant's first embodiment are carried over and a new design, free floating equalizer enhances the sharing of load and balancing between axles in addition to providing a softer ride by the addition of a spring means in place of the rigid pivotal connection of the equalizer. To maintain the equalizer in vertical alignment as the leaf springs shift laterally across the axles (longitudinally with respect to the chassis), a male fiber tube is bolted to the equalizer and is received by a female tube bolted to a hanger which surrounds the equalizer. Thus, as the equalizer moves in a vertical direction, the male tube slides freely within the female tube and maintains it in vertical alignment. A shock absorber extends through the male tube and connects between the equalizer and the hanger to dampen the oscillations of the equalizer as it is supported by an elastomeric spring member from the chassis itself. A mounting plate between the elastomeric spring member and the equalizer extends between a web fashioned in the third hanger and on opposite sides thereof to also help prevent any tendency of the equalizer to move longitudinally with respect to the chassis in response to lateral shifting of the leaf spring. The hanger which surrounds the equalizer also provides the mounting for torque rods on opposite sides of the hanger, thereby concentrating most of the suspension's components in a single hanger assembly which simplifies installation and adjustment of the suspension.
Applicant's third embodiment utilizes the same axle bracket assembly and torque rod arrangement to stabilize the axle as is found in the first and second embodiments. However, the leaf springs are rearranged to provide for the use of a free floating shackle assembly to secure an end of each leaf spring and thereby enhance the shifting and balancing of load between the axles in combination with applicant's improved axle bracket assembly and torque rod stabilization. Applicant's prior U.S. Pat. No. 4,131,297 issued Dec. 26, 1978, the disclosure of which is incorporated herein by reference, shows a similar leaf spring arrangement along with a free floating shackle assembly. That patented suspension system is an excellent one which provides parallelogram stabilized axles and a shackle assembly using elastomers for securing the ends of the leaf spring thereto. In the present invention, applicant uses his new design single torque arm and axle bracket assembly to stabilize the axle, thereby eliminating the requirement for parallelogram stabilizing including a radius rod at the center of the vehicle. Furthermore, applicant's present invention provides a unique rotatable mount in the shackle assembly which permits great flexibility in the leaf springs and which also eliminates the requirement for the elastomeric spacers of applicant's prior design. Each bushing assembly includes a fiber sleeve member which interfaces between the leaf spring mount and a pivot pin, thereby eliminating any metal to metal rubbing and significantly reducing both friction and wear in the shackle. While elastomer spacers provide excellent service, there is no doubt that the continual flexing they experience would require them to be replaced, although infrequently, but at shorter intervals than the shackle assembly of applicant's third embodiment. Thus, applicant's present invention represents a significant improvement over his prior suspension, which itself is a significant improvement over the prior art.
Some of the features and benefits of applicant's suspensions have been mentioned above, and a fuller understanding may be gained by reading and examining the drawings and the detailed description of the preferred embodiment which follows.